Let’s do a full clean re-install; '''[http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All languages And Systems]''' {web link} Save the file. Then '''Close Firefox.''' Using your file browser, open the '''Programs Folder''' on your computer. '''Windows:''' C:\Program Files C:\Program Files (x86) '''Mac:''' Open the "Applications" folder.<br>https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac '''Linux:''' Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install [https://support.mozilla.org/en-US/kb/install-firefox-linux Firefox on Linux]. If you downloaded and installed the binary package from the [http://www.mozilla.org/firefox#desktop Firefox download page,] simply remove the folder Firefox in your home directory. '''Do Not''' remove the profiles folder. Look for, and rename any '''Mozilla''' or '''Firefox''' program folders by adding '''.old''' to them. Do not rename the '''Mozilla Thunderbird''' folder if there is one. After rebooting the computer, run a registry scanner if you have one. Then run the installer. If all goes well, remove the OLD folders when you are done. --------- If there is a problem, start your '''Computer''' in safe mode and try again. '''[http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting The Computer In Safe Mode;<br>Free Online Encyclopedia]'''

You may have a problem with the disk permissions which make it impossible to install an already downloaded update. Try to repair the disk permissions. * http://www.howtogeek.com/195912/how-when-and-why-to-repair-disk-permissions-on-your-mac/ Mac: /Applications/Firefox.app/updates/0 Mac: /Applications/Firefox.app/Updated.app